Diesel engine "hunting" at idle, what can be the cause ?

[BartW]

1,5 year ago we had a major rebuild on our STBD engine, (including new engine Blok, crankshaft, pistons, liners , etc…)
It’s a 1991 Man D2842 LE402 (12cyl 1100HP)

Before the rebuild, at idle (650…700 rpm) the engine sounded as running on 6 cylinders

During the rebuild the mechanical injection pump went to a Bosh service center in Belgrade Serbia
The service center confirmed (?) that the pump is setup to run at 6cylinders at idle
So after the rebuild the engine ran and sounded as before

Last winter we had a rebuild on the Port engine, (a lot less dramatic, just new pistons and liners, ..)
And in order to have a perfect matching pair, the MAN guy send both injection pumps to Bosh service center in Koper Slovenia,
In the past he had worked with them a few times and had much better communication and service from them.

Now after this rebuild,
The Port engine is running very smooth at idle, (as before)
And the STBD engine, is ‘hunting’ at a even lower freq than before
Period is a bit less than 1 sec
During manouvring, we can feel the “pulsing” behaviour of the engine
so even under load the engine is “hunting”

What could be the cause of this ?
First idea is bad functioning governor, but why didn’t these service centers not find that ?
Our MAN guy is talking with them,

As I have got some very good and correct advice and or suppositions from them in the past,
I’d like to hear the forum specialist’s opinion ?

 

[volvopaul]

Post me a pic of the rear of the pump where the throttle shaft is , or it could have an adjustable throttle damper in which case it needs setting up .

 

[Latestarter1]

Bart,

Can you include picture of solenoid shutdown.

Just possible that your shutdown solenoid is holding the lever just slightly, please ask if your pumps have RSV or RQV governing, failing to release shut down lever 100% will create exactly the symptoms you have if you have RSV governor.

 

[Duster]

May not be relevant but older Ford based engines all did this, if the inline injector pump was low on oil or the oil had been thinned with diesel.

A simple pump oil change fixed it - for a while.

 

[BartW]

I'm not at the boat right now,
this is the only pic I can find from the pump,

the Bosch sticker is on the electric connection box from the shutdown solonoid
just above the solonoid you can see the rod with damper (?) that should be connected with the throttle drive mechanism,
this pic is taken when the hydraulic throttle drive mechanism was not yet back in place (after the rebuild)
other side of the rod pushes via the lever arm another rod, going to the governer side of the pump

the governer side of the pump is hidden under the intercooler, (no pic available unfortunately)

your sugestions are very much possible,
as there is a lot of "play" on this mechanism due to wear from vibrating
some time ago, I have replaced some of these pivot connections that were totally worn out, ...

I have send advice to Ilko, to check this mechanism...
and asc him if he knows its RSV or RQV
care to explain the meaning of these abbreviations ?

thank you all for the advice !

 

[superheat6k]

Can you see the throttle shaft hunting in tune with the engine fluctuations ?

Try gentle finger pressure on the linkage to see if you can stabilise the hunt.

You mention worn linkages. I think you may have answered your own question, but check also what VP suggests that the damper is set up correctly.

 

[Latestarter1]

Bart,

That sure is a big MW, and that damper lever flopping in the breeze cannot be correct, I will hunt out my old Bosch training manuals and see if I can find your setup.

Bosch RQV is a variable-speed (all-range) governor, The RSV governor is designed as a variable speed governor which functions to control the engine idle and maximum speeds.

RSV has good steady state control characteristics in the speed range however is nowhere as sweet as RQV particularly at idle governing where it can be prone to surge if not set 100% with no load on the shutdown lever.

In defence of the pump shop did your tec send the pump off with or without all the monkey motion shutdown levers attached?

 

[BartW]

and that damper lever flopping in the breeze cannot be correct,

Just to clarifie,
this pic was taken more than a year ago, just after the rebuild, in the workshop. (not all components in place yet)
at this moment everything is assembled as it should be,

I guess that the pump was send to the shop complete with the schutdown solonoid, because that first shop left that sticker on there (a year ago)
this pump went a second time to (another) Bosch shop a few months ago